Switching and display devices containing ferroelectric liquid-crystal mixtures (FLC displays) are disclosed, for example, in EP-B 0 032 362 (U.S. Pat. No. 4,367,924). Liquid-crystal displays are devices which, as a consequence of electrical switching, modify their optical transmission properties in such a way that incident (and possibly re-reflected) light is modulated in intensity. Examples are the known watch and calculator displays or liquid-crystal displays in the OA (office automation) or TV sectors (see also Liquid Crystal Device Handbook, Nikkan Kogyo Shimbun, Tokyo, 1989; ISBN 4-526-02590-9C 3054 and the papers cited therein).
These FLC displays are constructed in such a way that a ferroelectric liquid-crystal layer is enclosed on both sides by layers which are usually, in this sequence starting from the FLC layer, at least one alignment layer, electrodes and a limiting plate (for example made of glass). In addition, they contain one polarizer if they are operated in guest-host or reflective mode or two polarizers if the transmissive birefringence mode is used. The switching and display elements may contain further auxiliary layers, such as diffusion barrier or insulation layers.
The alignment layers, which comprise an organic (for example polyimide, polyamide and polyvinyl alcohol) or inorganic (for example SiO) material, together with a separation between the limiting plates which is chosen to be sufficiently small, bring the FLC molecules of the mixture into a configuration in which the molecules lie with their long axes parallel to one another and the smectic planes are arranged perpendicular or inclined to the alignment layer. In this arrangement, the molecules, as is known, have two equivalent orientations, between which they can be switched by pulse-like application of an electric field, i.e. FLC displays are capable of bistable switching. Response times are inversely proportional to the spontaneous polarization of the FLC mixture and are in the region of microseconds.
Surprisingly, it has now been found that polymers containing maleimide monomer units can advantageously be employed as alignment layers in liquid-crystal displays, in particular ferroelectric displays.
Polymers of this type have hitherto been employed as binders in photoresist materials, as described, for example, in U.S. Pat. No. 720,445, EP 0 140 273 and EP 0 234 327. However, their use as an alignment layer in LC displays, in particular FLC displays, has not previously been described.